As the cost of energy conversion is increased on a worldwide basis, extensive developments have been undertaken to make alternative energy sources available not only to industry but also to the home. Wind and solar energy have been harnessed in endeavors ranging from highly complex and elaborate prototype installations to the approaches of the home handyman. From these endeavors, there have developed a selection of viable wind and solar energy power generating devices which have become available to the consumer in the domestic marketplace. Each, necessarily, is an intermittently performing device, wind usually not being a steady state phenomenon and the energy of the sun being modified by factors of earth time and weather. As a consequence of this production intermittency, these systems generally serve an alternate power generating role supplementing that power conventionally available from utility companies.
To accommodate for the variable availability of energy for conversion, the alternate power sources are installed in conjunction with a storage media, typically in the form of batteries. Thus, energy may be harnessed and stored in the batteries during intervals of availability, then such stored energy is used at more convenient times. The type of battery conventionally employed with the alternate energy system is one of a "deep cycling" variety which can be repeatedly completely discharged and recharged essentially without damage. The batteries are typically employed in applications where steady current is to be used over a relatively lengthy period of time and they are structured having a lead-liquid electrolyte architecture. While these battery structures may be deep cycled over a relatively large number of cycles, their life spans are limited thereby such that it is desirable to retain thereat a relatively fully charged status. For this purpose, charging techniques are employed in a two-step arrangement wherein full power is applied to the batteries until they are charged, whereupon, a resistance is switched into the charging circuit to significantly reduce the amount of current into the batteries and provide a low level or "trickle" charging current. Such charging charge is often referred to as a "maintenance charge". Where such steady charging continues, even though the battery is at its ultimate charge capacity, the electrolyte therein may tend to boil, and thus to generate hydrogen gas which is explosive in free air. Further, electrolyte levels within the battery may diminish to expose the plates thereof to atmosphere and cause erosion. Of course, by imposing a resistance in the charging system, energy is lost.
Solar panels, for example of the photovoltaic variety, function to generate voltages and d.c. currents in response to sun activation and, thus, their outputs may be employed for storage battery charging. However, when coupled within a storage battery based system, complexities arise in achieving an optimized performance of such combinations. For example, when in operation, the panels are electrically coupled in charging relationship with the batteries. As such, the photovoltaic panels will assume the voltage level of the batteries and, consequently, the operational status of the solar panel is not determined readily by constant voltage monitoring techniques. To determine the operational status of the panels, the conventional practice has been to interrupt the charge cycle and to test the panels in isolation in accordance with some prearranged timed schedule. Such timing, unless meticulously maintained, often will be inadequate with the result that back current activity may ensue. To correct for such back discharge, typically, line current blocking diodes are employed which are power consuming heat dissipators.
Those designing photovoltaic solar panel based alternative energy sources also encounter an operational phenomenon wherein the panels will exhibit an operational voltage level upon being initially activated by the sun. However, while exhibiting acceptable voltage levels, they will not generate current for a period of time following this initial witnessing of adequate voltage levels. Thus, time based factors of safety generally are required in establishing operational periods in which the panels are coupled within the system. These time based systems are not constant in nature. In this regard, the amount of sun available during any period of the day will vary with the seasons, as well as with weather during those changing seasons. Thus, it is necessary to continuously adjust the time control aspects of any solar based alternative energy system. This timing aspect represents a particularly critical input when considering the periodicity of winds which may be used in conjunction with windmill powered alternate energy sources. Here the timing must be very carefully adjusted with respect to known but variable wind histories at the point of installation. Windmills also pose a safety problem in terms of their maintenance where any possibility for back currents may occur. For example, the devices very often will "motor" or be driven by such currents, a condition which may pose hazards to maintenance personnel.
The straightforward timing approaches to controling the employment of alternate energy sources within a hybrid power supply system also is prone to undue complexity where it is desired to establish priorities between the election of utility power and the supplementary source. When priorities are to be given to that supplementary or alternate source, very close maintenance of the timing system and a continued awareness of weather-atmospheric conditions must be provided. Of course, such close attention to systems which traditionally have been at best ignored by the homeowner does not represent a practical approach.